20 - Manipulating the Estrous Cycle

Question 1

Advantages of controlling the estrous cycle in livestock (7)

Answer 1

1. Saves time & labour in estrus detection, facilitates AI
2. allows for group management of breeding animals
3. permits group management of gestating animals
4. avoid losses of young at birth by providing care & supervision
5. provides uniform groups of young
6. facilitates stricter disease control
7. essential for reproductive technologies (fixed time AI, ET, IVF)

Question 2

Three methods of hormonal manipulation of the estrous cycle ***

Answer 2

1. prolong the luteal phase (administer progestins)
2. shorten the luteal phase (administer PGF2a)
3. control follicular development and ovulation (GnRH, FSH or LH)

Question 3

Progestins used in cattle

Answer 3

• CIDR (controlled internal drug release)
• PRID (progesterone releasing internal device)
• melengesterol acetate (MGA): oral progestin

Question 4

What is typical CIDR protocol

Answer 4

• CIDR inserted and removed after 7-8 days
• 1 day prior to CIDR removal PGF2a injection causes CL to regress (if present)
• cows/heifers will come into heat over next few days

Slide 12

Question 5

What is typical MGA protocol

Answer 5

• Feed MGA for 14 days
• CL regresses while oral progestin maintains anestrus
• 1st estrus after MGA withdrawal less fertile (skipped)
• bull introduced 14 days after MGA withdrawal to breed on 2nd estrus

Slide 13

Question 6

How do we prolong the luteal phase in pigs and horses

Answer 6

Oral progestin altrenogest
- Altrenogest (Regu-mate/Matrix) added to feed for 14 to 18 days
- CL regresses while oral progestin maintains luteal phase
- female comes into heat 3-7 days after withdrawal and can be bred

Slide 15

Question 7

How do we shorten the luteal phase

Answer 7

• Administer PGF alpha (PG) or analogue
• cause the CL to regress

Question 8

Slide 17

Answer 8

Important: effectiveness of PGF2a at different stages

Question 9

Slides 18,19

Answer 9

Common PG protocols, periods of PGF2a sensitivity in diff species

Question 10

Lactational anestrous in sows

Answer 10

• Sow will not return to estrus while nursing a full litter
• following appropriate lactation period (3-4 weeks) removal of litter will result in return to estrus 4-7 days later

Weaning controls estrus (slide 21)

Question 11

How do we induce parturition in sows? Why

Answer 11

• administer PGF2a after 111 days of gestation: sows farrow 8-24 hours later

Allows for better use of labour to supervise farrowing, batches of synchronized sows at weaning that will come into estrus together

Slide 22

Question 12

Equine seasonality

Answer 12

• seasonal polyestrous (long-day breeders)
• 90% of mares are seasonal

Generally, in northern hemisphere:
Cyclic April-September
Transition to anestrus Oct-Dec
Deep anestrus Jan-Feb
Transition to cyclicity Mar-Apr

Question 13

How do we manipulate seasonality in mares

Answer 13

Artificial photoperiod
- Start dec 1st: 16 light/8 dark
- Ovulation occurs 35-60 days after
- breeding season started feb 15th

Question 14

What are light masks in horses

Answer 14

New technology that has comparable results to conventional barn lighting approach (manipulate season)

Question 15

Slide 28

Answer 15

Synchronizing ovulation in cattle (presynch & ovsynch)